1. Field of the Invention
The present invention relates to an electric generation control system for use on a hybrid vehicle having a propulsive electric motor energizable by a battery and an electric generator actuated by an internal combustion engine for energizing the propulsive electric motor.
2. Description of the Related Art
Growing concern in recent years over environmental protection has led to various efforts to develop for practical applications electric vehicles which have a propulsive electric motor energizable by a battery to transmit drive forces to drive wheels for propelling the electric vehicle. One of the important requirements for such electric vehicles to satisfy is that the range which they can travel without recharging the battery be maximized and the discharging of the battery be minimized for increased battery service life.
One solution disclosed in Japanese laid-open patent publication No. 3-169203 is a hybrid vehicle carrying an electric energy generating apparatus having an electric generator and an internal combustion engine for actuating the electric generator. Electric energy generated by the electric generator is supplied to charge a battery or to energize a propulsive electric motor.
While the disclosed hybrid vehicle is running, the battery energizes the electric generator to operate as an electric motor in a motor mode to start the engine. After the engine has been started, the electric generator is switched from the motor mode to a generator mode in which it is actuated by the engine to generate electric energy, and then the engine is warmed up. Thereafter, the electric generator is operated to generate an appropriate amount of electric energy depending on an operating condition of the hybrid vehicle, such as the vehicle speed of the hybrid vehicle, and the generated electric energy is supplied to the battery or the propulsive electric motor.
The electric generator is operated to generate the electric energy as follows: Depending on an operating condition of the hybrid vehicle, such as the vehicle speed of the hybrid vehicle, a target generated output for the electric generator is obtained from a predetermined data table or the like. Then, the engine is controlled to produce a power output (drive forces to actuate the electric generator) which corresponds to the target generated output. The engine is controlled by regulating, with an actuator or the like, the opening of a throttle valve (intake air control valve) of the engine into a throttle valve opening corresponding to the target generated output. The generated output of the electric generator is also increased or reduced into agreement with the target generated output by controlling an output current from the electric generator with an inverter circuit or the like. The above generator control process is carried out from time to time to cause the electric generator to generate an amount of electric energy depending on the operating condition of the hybrid vehicle.
In the above generator control process, once the target generated output is determined, the electric energy generated by the electric generator can be controlled substantially on a real-time basis according to the target generated output. Therefore, the electric energy generated by the electric generator can be controlled to catch up with the target generated output even when the target generated output varies from time to time. However, after the target generated output has been determined, the power output control of the engine tends to suffer a delay, from the electric energy control of the electric generator, until the engine produces a power output corresponding to the target generated output. Specifically, the power output control of the engine is carried out by mechanically moving the throttle valve with the actuator to control the opening of the throttle valve. When the target generated output varies, the actuator starts actuating the throttle valve to control its opening to cause the engine to produce a mechanical power output corresponding to the target generated output which has varied, but a certain time is required before the opening of the throttle valve eventually reaches an opening corresponding to the target generated output. Even after the opening of the throttle valve has eventually reached an opening corresponding to the target generated output, a certain time is further required until the amount of intake air introduced into the engine reaches an amount corresponding to the target generated output. Consequently, when the target generated output varies, if the electric energy control of the electric generator and the power output control of the engine start to be effected simultaneously according to the target generated output which has varied, then the electric energy generated by the electric generator is immediately controlled, but there is a delay time until the actual power output of the engine reaches a power output corresponding to target generated output which has varied. With such a delay time, the electric energy generated by the electric generator is inappropriate with respect to the actual power output of the engine after the power output control of the engine is effected until the actual power output of the engine reaches a power output corresponding to target generated output which has varied. As a result, the engine suffers an unwanted load variation, and tends to operate unstably. For example, when the target generated output is increased, the electric generator is immediately electrically controlled to increase its generated output, but the engine requires a certain period of time until its power output reaches a power output commensurate with the generated output of the electric generator. During such a certain period of time, the electric generator generates an electric energy output higher than the electric energy output that matches the actual power output of the engine. Therefore, the engine suffers an excessive load, and operates unstably.
If the operation of the engine becomes unstable, then the engine is caused to emit unwanted harmful exhaust gases or vibrate undesirably.
The delay time of the engine control at the time the target generated output varies differs with the rotational speed of the engine and also differs depending on a change in the rotational speed of the engine which is caused by the variation in the target generated output and whether the rotational speed of the engine increases or decreases due to the variation in the target generated output.